I can't keep my armature in pose mode when selecting another object
This has to do with how editors/modes have changed in 2.8 (presumably related to multi object editing?)

There is an option in the edit menu called Lock Object Modes which forces the mode to be consistent across all objects. If an object doesn't support the current mode then it cannot be selected. Disabling this mode allows leaving the armature in pose mode and then selecting the mesh: